Laser beams and other light beams are used today in a wide variety of applications ranging from communications to dentistry. In the field of dentistry, for instance, one use of laser light is to cure or harden resins used as filling material in teeth. As used herein, "light beam" denotes not only a laser beam but also any beam of coherent light, collimated light, semi-collimated light, or high-intensity light.
Light beams are typically generated by specialized equipment which varies from one application to another. However, many light beam generators are subject to two major drawbacks. First, light beam generators often require a substantial investment. Laser generators, for instance, may require a substantial initial investment, and additional funds are often required to meet ongoing power, cooling, calibration, and maintenance needs.
Some conventional systems attempt to avoid the expenses associated with multiple laser generators by making the generator somewhat portable. In the field of dentistry, for instance, one use of laser light is to cure or harden the resins used as filling material in teeth. To permit the availability of laser light in multiple dental operatories, some conventional systems are designed to be moved on a cart or similar device from room to room.
However, such portable generators have drawbacks. First, significant amounts of time may be required to relocate the laser generator. Second, it is often inconvenient to have the generator in the operatory. Operatories have limited space, which is already in demand for use by other equipment and by patients and dental personnel. Laser generators may also produce undesirable heat. Finally, such portable generators may typically only be used by one person at a time.
Another drawback of light beam generators is that even if a generator is tailored to a specific application such as dentistry, further adjustments to the light beam are often needed to satisfy particular conditions. For instance, the light beam's geometry, spectral characteristics, or strength must often be altered after the beam emerges from the generator.
Light beams may be altered through the use of optical surfaces. An "optical surface" is a surface which reflects, refracts, diffracts, filters, polarizes, or performs some combination of these operations upon light. Familiar examples of optical surfaces include mirrors, lenses, filters, and gratings. Optical surfaces need not be planar, but particular accuracy considerations arise in connection with those that are, as explained below.
Multiplexing addresses both the high cost and the inflexibility of light beam generators. As used herein, "multiplexing" a light beam includes engaging the light beam with one or more optical surfaces. Thus, multiplexing may include any of the following operations singly or in combination: switching, splitting, filtering, polarizing, passing the beam through a lens, or other operations performed with optical surfaces.
Multiplexing is performed by moving at least one optical surface from a passive position, in which the optical surface does not intersect the light beam, to an active position, in which the optical surface intersects the light beam in a desired manner. Multiplexing may also include movement of one or more optical surfaces from active to passive positions. An optical surface which intersects the light beam is said to engage the light beam, regardless of whether the optical surface is in the active position.
Two forms of multiplexing which address the high cost of light beam generators involve switching or splitting the light beam between several users. Beam switching involves directing the entire light beam first to one user and then to another. Switching may be performed with a group of fully reflective mirrors, each of which is arranged to direct the light beam toward a different user if it engages the beam. Beam splitting, by contrast, involves providing discrete fractions of the beam to multiple users at substantially the same time. Splitting may be performed with partially reflective mirrors which direct a portion of the beam toward one user and permit the remainder of the beam to continue toward another user. With either switching or splitting, however, the light beam generated by a single generator is divided between multiple users, thereby lowering the cost per user.
Multiplexing addresses the inflexibility of light beam generators by permitting the selective processing of a light beam before the beam reaches its target. By interposing filters, lenses, and other optical surfaces between the generator and the target, the light beam may be suitably modified.
Thus, multiplexing is a central requirement of many light beam applications, both to reduce their cost and to maximize their effectiveness. A central requirement of multiplexing, in turn, is the ability to accurately and cost-effectively move an optical surface between active and passive positions relative to a light beam.
Although conventional multiplexing systems differ in their approach, many are quite complex. In particular, many known systems employ stepper motors, complicated mechanical linkages, sophisticated electronics, and other intricate components to position the optical surface. Such positioning mechanisms often drive up the cost of the multiplexing apparatus and may also reduce reliability.
Accurate multiplexing is generally necessary to ensure adequate performance. Accuracy is essential in applications using high power laser beams, because people or equipment may be injured by a misdirected beam. One important measure of accuracy is whether the optical surface has a steady and predictable active position. If the optical surface does not hold steady, the engaged light beam may be reflected improperly, or may not be properly focused. Similar problems may arise if the optical surface does not always arrive at a predictable active position in relation to the light beam. Conventional systems based on intricate components often fail to provide steady and predictable active positions when these components fall out of calibration or fail completely.
In addition, it is difficult to design "fail-safe" devices using the complex positioning mechanisms of known systems. A fail-safe device is one whose behavior upon power failure provides a reliable measure of safety. A fail-safe laser multiplexer, for instance, might be designed so that localized failure of power to a mirror positioning mechanism always disengages the mirror, thereby permitting the laser beam to be directed toward a known safe location pending appropriate steps by the user. Such a fail-safe laser multiplexer is difficult to design using only a stepper motor for mirror positioning because such motors often freeze in place when they lose power. Adding additional linkages to force disengagement may add considerably to the multiplexer's complexity and expense.
Another important measure of accuracy is whether the light beam is misdirected as the optical surface travels between the passive and active positions. Of course, the light beam generator may be turned off while the optical surface moves. In practice, however, the generator is often left on while the optical surface moves, so it becomes important for the optical surface to move in a way that reduces or eliminates misdirection of the engaged light beam.
A serious drawback of conventional designs is their inaccuracy while the optical surface moves between the passive and active positions. The drawback is perhaps most readily apparent in connection with planar optical surfaces such as mirrors, which are widely used.
For example, one conventional design employs a mirror mounted on a rotary stage. Even if the mirror forms the correct angle of incidence with the light beam in the engaged position, the rotary stage is inherently inaccurate because the angle between the rotating mirror and the light beam changes as the stage rotates in or out of the engaged position. Because the mirror engages the light beam while the stage is in motion, the changing angle between the mirror and the light beam misdirects the light beam.
Another conventional design, which employs a translation stage, has a similar inherent problem. In this design, the mirror is mounted at approximately a forty-five degree angle to the light beam, on a translation stage which moves linearly at right angles to the light beam. Unlike the rotary stage, the translation stage design ensures that the mirror always engages the light beam at the same angle of incidence (forty-five degrees) during the transition between the active and passive positions. However, the location within the light beam where the mirror hits the beam moves as the stage translates in or out of the active position. Because the mirror plane does not always "cut" the light beam at the same distance from the beam's origin, the beam is reflected inaccurately.
Thus, it would be an advancement in the art to provide a cost-effective and accurate apparatus and method for engaging and disengaging an optical surface with a light beam.
It would be a related advancement to provide such a multiplexing apparatus and method that does not rely on stepper motors, complicated mechanical linkages, sophisticated electronics, or other intricate components to position the optical surface.
It would also be an advancement in the art to provide an apparatus and method that does not misdirect the light beam during the transition between passive and active optical surface positions.
It would be a further advancement to provide a fail-safe apparatus and method that reliably positions the optical surface in a safe position in the event of a power failure.
Such an apparatus and method is disclosed and claimed herein.